The present invention relates to a biodegradable lubricant composition, notably intended to be incorporated as an oil phase with high lubricating power in a drilling fluid or mud. The invention also relates to the use of this composition as a continuous oil phase of a oil drilling fluid or mud as a reverse emulsion, which is particularly well suitable for deeply buried boreholes, so-called offshore holes in deep water and/or for sidetracked holes or with a long offset.
Certain sites, like extensive civil engineering work projects, require large amounts of lubricants, which are capable of being partly discharged into the environment. This is notably the case of drilling fluids and muds. The borehole occupies a primordial place in oil field development and production with a trend to increasingly deep drilling operations. The technology of drillings is in constant development, whether on land or on the seabed, in particular in what is called deep offshore, but also more recently in horizontal or sidetracked drillings, where, by successive inclinations by one or two degrees, the trajectory of the well is curved, with which horizontal offsets of at least more than one kilometer or even of more than ten kilometers relatively to the head of the well may be attained. The friction forces which are exerted are therefore increasingly large, whence the increased importance of the lubricant properties of the drilling fluid.
In a known way, the drilling technique uses a bit attached to the end of drilling rods which, driven into rotation, digs the well by crushing the rocks. As the drilling progresses, bits with increasingly small diameters are used and at each step, the well is consolidated with a steel tube called a casing, which is lowered into the inside of the hole, and then fixed by cement. During the drilling, a drilling fluid is put into circulation, with injection into the bit and expulsion of the latter in the area in contact with the rock, and then brought up to the top of the well through the annular space separating the drilling rods from the casing.
This fluid generally fulfils the following main functions:                cooling the bit,        reducing the metal-metal friction forces between the casing and the drilling rods, and the metal-rock friction forces both at the bit and in the ring-shaped area, since the fluid flows upwards, loaded with crushed rock particles so-called “cuttings” in the art,        evacuating the rock cuttings towards the outside,        generating pressure on the walls of the hole in order to prevent their collapse, and        balancing pressures between the bottom of the well and the surface, in order to keep control of the well and to avoid an explosion (“blow out”).In the case of offshore drillings in deep water, the encountered water temperatures close to 4-5° C., require good control of the viscosity of the drilling fluids at these low temperatures.        
Various types of drilling fluids or muds have been used in the past, such as fluids with water, containing water and additives for increasing the viscosity, fluids with oil and emulsions of the water-in-oil type or reverse emulsions or of the oil-in-water type, as described in particular in U.S. Pat. No. 2,816,073. This document indicates that the oil phase may be formed by different hydrocarbon fractions, such as kerosene cuts and gas oils and strongly alkylated and branched petroleum cuts.
In muds with water (water base mud, abbreviated as WBM), the drilling fluid is water; muds with water are generally reserved for not very technical applications and for onshore drillings (on land), or very shallow (a few meters) offshore. In muds with oil (oil base mud abbreviated as OBM), the drilling fluid is a hydrocarbon fluid selected from various compounds available on the market.
These drilling fluids with oil are classified into three large categories:                Group I comprises strongly aromatic drilling fluids containing from 5 to 30% of mono-aromatic and/or poly-aromatic compounds stemming from the refining of crude oils, i.e. gas oils and conventional mineral oils;        Group II comprises moderately aromatic drilling fluids stemming from the refining of crude oil and containing from 0.5 to 5% of mono-aromatic and/or poly-aromatic compounds such as unconventional or slightly hydrotreated mineral oils often called Low Toxicity Mineral Oil (LTMO);        Finally, Group III comprises slightly aromatic drilling fluids, i.e. containing less than 0.5% of total aromatics including less than 10 ppm of polyaromatics. These fluids generally stem from chemical synthesis or severely hydrotreated, hydrocracked or hydroisomerized refined cuts. They may also be compounds of synthetic paraffins stemming from the Fisher Tropsch process, polymerized olefins (Internal Olefins or 10, Linear Alpha Olefins or LAO, and Poly Alpha Olefins or PAO) as well as of esters.        
The fluids of Group III are said to be synthetic according to the definition of the OSPAR protocol according to Ruling 2000/3 “on the Use of Organic-Phase Drilling Fluids (OPF) and the Discharge of OPF-Contaminated Cuttings”; these fluids of Group III are preferred by the operators not only for their heat stability, their resistance to oxidation, their low toxicity related to their low aromaticity, their non-irritating nature and respectful of the environment but also for their observance of safety requirements, notably by a high flash point and lesser volatility. It is known that the use of petroleum cuts (notably Groups I or II) which have high contents of aromatic compounds in drilling muds has high risks of toxicity particularly for marine life, if it is chosen to discharge them into the sea, for example in the case of offshore drillings. The deposit of significant amounts of these products on the seabed has led the bordering countries to adopt increasingly strict legislations, forcing the operators of offshore oil drillings, notably in the North sea, to search for products as biodegradable and non-toxic as possible.
In EP 667 890, a drilling fluid is described having a continuous oil phase consisting of a mixture of n-alkanes having between 10 and 20 carbon atoms, essentially free of other types of hydrocarbons. Now, it is noticed that this fluid has a too high pour point for use in a low temperature area, typically less than or equal to 5° C. Esters based on saturated (notably C12-C14) or unsaturated monocarboxylic acids and on monofunctional alcohols have been proposed as an oil phase in reverse emulsion drilling muds, notably in EP 374 671, EP 374 672 and EP 386 636.
Other synthetic compounds such as PAOs (polyalpha-olefins) or LAOs (linear alpha-olefins), obtained by oligomerization of olefins, may also be used in a mixture with the previous compounds. But these compounds have very poor biodegradability in particular anaerobic biodegradability. Further, the use of all these synthetic products considerably increases the price cost of the drilling fluids into which they are incorporated. EP 1 282 675 proposes a lubricant composition, notably usable as an oil phase of a reverse emulsion drilling fluid, having flow properties and lubricant power suitable for severe conditions of use of this fluid, while preserving quite acceptable biodegradability; this fluid comprises from 60 to 95% by mass of a hydrocarbon mineral cut substantially free of aromatic compounds, the n-paraffin content of which is less than or equal to 10% by weight and the iso-paraffin content is greater than or equal to 35% by weight and 5 to 40% by mass of at least one fatty acid ester which preferably is an ester of 2-ethyl hexanol and rapeseed fatty acids.
The present invention relates to a lubricant composition, notably usable as an oil phase of a drilling fluid, having flow properties and lubricant power particularly well suited to severe conditions of use of this fluid, while preserving its biodegradability comprising a mixture of a major amount of a hydrocarbon mineral cut practically free of aromatic compounds and of a composition consisting in majority of fatty acid(s). For this purpose, the object of the present invention is a biodegradable lubricant composition, based on a hydrocarbon mineral oil and on fatty acid(s) characterized in that it comprises a major amount, comprised between 99.95 and 90% by mass, preferably between 99 and 95% by mass, of a slightly aromatic hydrocarbon oil, preferably non-aromatic oil (an aromatic content measured according to IP391 of less than or equal to 1% by mass, preferably less than or equal to 0.1% by mass), and a minor amount, comprised between 0.05 and 10%, preferably between 1 and 5% by mass, of a composition of in majority saturated and/or unsaturated C16-C22 monocarboxylic fatty acid(s) optionally in a mixture with resin acids (unsaturated monocarboxylic, polycyclic notably tricyclic, acids).
In the sense of the present invention, by a composition in majority consisting of C16-C22 monocarboxylic acid(s), is meant any composition for which the concentration of C16-C22 monocarboxylic fatty acid(s) accounts for 80% to a 100% of the total mass of the composition. Generally, the remainder of the composition comprises monocarboxylic fatty acids, the hydrocarbon chain of which has at least 16 carbon atoms and/or more than 22 carbon atoms. The compositions consisting in majority of C16-C22 monocarboxylic fatty acid(s) optionally comprise resin acids. The resin acid concentration preferably accounts for up to 10% by mass of the acids (fatty acids+resin acids) of resin acid(s) and advantageously less than 5% of the total mass of the acids (fatty acids+resin acids).
The compositions consisting in majority of C16-C22 monocarboxylic fatty acids may for example be obtained by hydrolysis of natural and/or genetically modified vegetable oils, of animal fats; mention may be made of the fatty acids derived from peanut, palm, olive, rapeseed, cotton, maize, sunflower, soya bean, flax, tallow oils and/or derived from lard. Among the resin acids, mention may be made of abietic, dihydroabietic, tetrahydroabietic, dehydroabietic, neoabietic, pimaric, levopimaric, parastrinic acids. The compositions consisting in majority of fatty acids and containing resin acids may be obtained by distillation of tall oil, a by-product of the making of wood pulp; and one then refers to TOFA which is the acronym of tall oil fatty acids. TOFAs are for example marketed by TOTAL ADDITIFS & CARBURANTS SPECIAUX under the trade names PC 30, PC 31 and PC 32. In these commercial mixtures, the resin acids generally account for less than 10% by mass and advantageously less than 5% of the total mass of the acids (fatty acids+resin acids). The preferred compositions based on fatty acids are of natural origin, i.e. in the sense of the present invention of vegetable and/or animal origin and not of fossil origin.
The object of the invention is also biodegradable lubricant compositions, based on hydrocarbon oil and ester(s) of glycerol and tall oil fatty acid(s), characterized in that it comprises a major amount, comprised between 99.95 and 90% by mass, preferably between 99 and 95%, of a hydrocarbon mineral oil substantially free of aromatic compounds and a minor amount, comprised between 0.05 and 10% by mass, preferably between 1 and 5%, of a composition in majority of ester(s) of tall oil fatty acid(s) and of glycerol. The ester(s) of tall oil fatty acid(s) and of glycerol may be obtained by esterification of tall oil fatty acid(s) as defined earlier and of glycerol. The slightly or even non-aromatic hydrocarbon oils generally stem from cuts of petroleum products from refineries and the methods for obtaining them generally apply refining methods such as fractionation and purification which allows a reduction in the aromatic level.
The purification typically consists in hydrodesulfurization and/or hydrogenation in order to reduce the sulfur content, in certain cases for removing the sulfur present and reducing or removing the aromatic compounds (de-aromatized oils) and the unsaturated compounds. Conventionally, aliphatic hydrocarbon mineral oils are obtained from virgin petroleum cuts or from cuts from reforming and distillation processes, which have been hydrosulfurized and fractionated beforehand. The de-aromatized mineral oils are obtained from hydrosulfurized, fractionated and hydrogenated products for saturating the aromatics present, hydrogenation may occur before the final fractionation.
The slightly or even non-aromatic hydrocarbon oils may be of mineral origin (from petroleum but also from coal (Coal to Liquid) from gas (Gas to Liquid)) and/or from an animal and/or plant renewable source such as from the biomass (BtL), for example from hydrotreatment and isomerization of esters of vegetable oils. The hydrocarbon oils of the lubricant composition according to the invention generally have boiling temperatures in the range from 220 to 350° C.; mineral oils from cuts having narrower boiling ranges being generally preferred. Preferably, the lubricant compositions according to the invention are liquid at room temperature.
The object of the present invention is therefore to propose lubricant compositions having good biodegradability properties usable as an oil phase in drilling muds, for example as a direct emulsion (o/w) or as a reverse emulsion (w/o). The advantages provided by the compositions according to the invention are of providing a satisfactory compromise between lubricating power and biodegradability, by using them for obtaining a lubricant composition notably incorporated as an oil phase in an drilling fluid, at an optimum cost as compared with that of fluids based on very specific synthetic oils. These compositions also allow savings as regards the price cost of drilling fluids formulated with the latter and maintaining the pour point and the low temperature kinematic viscosity (below 5° C.) at relatively low levels.
Preferably, in the lubricant composition according to the invention is found a hydrocarbon cut, for example of mineral origin, consisting in majority (i.e. of more than 50% by mass) of hydrocarbons having between 13 and 22 carbon atoms. Further, it advantageously has a content of aromatic compounds of less than or equal to 0.1%, and advantageously of less than or equal to 0.01% by mass. The lubricant composition according to the invention generally has a flash point (according to the NF M 07019 method) of greater than or equal to 90° C., preferably greater than or equal to a 100° C. The lubricant composition according to the invention preferably has a kinematic viscosity at 40° C. (according to the NF T 60100 method) comprised between 1.8 and 4 mm2/s and even more advantageously of less than 2.5 mm2/s. The lubricant composition according to the invention has an aerobic biodegradability rate of more than 20% measured according to OECD 306.
Another object of the invention is the use of the lubricant composition according to the invention as defined earlier as a continuous oil phase of a drilling fluid or mud as a reverse emulsion, or as an oil phase dispersed in a continuous aqueous phase; in the case of reverse emulsions, the oil phase generally represents between 60 and 90% by volume of the drilling fluid. The drilling fluid is generally used in combination with functional additives depending on the type of application of the mud. One of the main functional additives of the mud or of the fluid is the weighting agent essentially consisting of barite. Other additives may be used in combination, which are emulsifiers, wetting agents, viscosifiers, filtrate reducing agents, particulate agents for forming gravel filters, supporting agents for maintaining open fractures hydraulically in underground formations, such as calcium carbonate or graphite.
Preferably, the drilling mud or fluid according to the invention comprises from 30% to 95% by mass of the lubricant composition according to the invention as defined earlier and from 5% to 70% of functional additives of said mud. The compositions of these muds vary depending on whether they will be used as a drilling fluid or as a fluid for fracture of underground formations. These drilling muds or fluids are particularly suitable for offshore drillings in deep water. The drilling muds may be prepared for example by mixing at room temperature the various components listed earlier.
It is also possible to prepare a concentrate comprising mineral oil and fatty acids and/or esters of glycerol and fatty acids, as defined earlier containing more than 40% by mass of fatty acids and/or esters of glycerol and fatty acids (and therefore less than 60% by mass of hydrocarbon mineral oil) by mixing these constituents, for example at room temperature, and then during the preparation of the drilling mud or fluid on site, to add the hydrocarbon oil and the other ingredients.